notmuchsync default behavior change (was: notmuchsync: handling of the deleted tag)

[Sebastian Spaeth]

On 2010-09-22, Rob Browning wrote:
> In general, I think that until/unless notmuchsync can be more assured of
> doing the right thing, and in particular, if the deleted tag is likely
> to become official, notmuchsync should default to not setting it.
> ...or at least, I'd prefer that.  Then I can add --tag-deleted if/when I
> want to.  Of course defaulting to --tag-deleted would also be OK, as
> long as there's a --no-tag-deleted.

notmuchsync does not want to delete anyones' e-mails by accident and
although I believe that syncing the "deleted" tag should usually be
safe, I can think of situations with multiple copies of a mail where
things could go wrong. I therefore disabled syncing of the maildir flag
"trashed" and the notmuch tag "deleted" by default. It has to be
explicitly be enabled with the new --sync-deleted option.

Sebastian

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For reference, this could be a szenario where things turn out bad:

- Send a mail with FCC to your Sent folder and BCC yourself. You have
then 2 mail copies with the same mail id (1 notmuch entry)

- "Expire" your BCC copy via some mail/webclient, it gets maildir flag
"T"

- notmuch --revsync will examine new mails and in case the BCC copy is
what notmuch points to, notmuchsync will then add the notmuch tag
"deleted" to that mail id.

- notmuchsync --prune deletes the BCC mail copy but does not remove the
  "deleted" tag in the notmuch db (it probably should for safety
  reasons).

- 'notmuch new' will now recognize the BCC copy as removed and point to the
  "Sent/FCC" copy as the current file, but it still carries the "deleted"
  tag for the mail.

- notmuchsync --prune will happily delete your Sent/FCC copy of the
  mail, or notmuchsync --sync will mark your Sent/FCC copy with the
  "expired" maildir flag.
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